Lecture 1ab

Question 1

Why peas?

Answer 1

1. Can be grown in large quantities
2. They have large number of offspring
3. Short germination times
4. Controlled reproduction
5. Lots of characteristics (color, size, shape, etc.)

Question 2

What is the difference between cross pollination and selfing?

Answer 2

Cross pollination: brush pollen from anther to stigma of another plant, cut off immature anthers to prevent selfing

Selfing: transfer of pollen from anther to stigma of same plant

Question 3

How was the blending theory disproved?

Answer 3

• When crossing monohybrid true breeding parents, one trait disappears in the F1 –> some traits are recessive and some are dominant
• Recessive traits are not gone, they reappear in F2

Question 4

What is a test cross?

Answer 4

Unknown organism is crossed with homozygous recessive organism and offspring is examined to see if unknown organism is homo or hetero

Question 5

What is the law of segregation of alleles for a single trait?

Answer 5

• Alleles separate into different cells during gamete formation
• There is only one allele of a gene in each gamete
• Occurs because of separation of homologous chromosomes during Meiosis I
• Two alleles for ONE gene will separate during gamete formation

Question 6

What is the law of independent assortment for multiple traits?

Answer 6

• How one allele segregates does not affect how another allele segregates (in dihybrid cross for example)
• Depends on how homologous chromosomes line up during prophase of Meiosis I –> many different combinations possible
• Assumes genes of interest are on different chromosomes or if they are on the same chromosome then crossing over occurs
• Alleles for two genes will partition into gametes independently

Question 7

Define genome

Answer 7

The full haploid set of an organisms genes which define an organism, does not include plasmids

Question 8

Haploid vs diploid?

Answer 8

Haploid: one set of chromosomes (1 copy of every gene, one allele)

Diploid: two sets of chromosomes (2 copies of every gene, two possible alleles)

Question 9

Homologous chromosome vs dyad vs bivalent (tetrad)?

Answer 9

Homologous chromosomes: two duplicated chromosomes carrying same genes but not necessarily the same alleles. Only found in diploid cells.

Dyad: duplicated chromosome, composed of sister chromatids attached at centromere, same genes, same alleles

Bivalent (tetrad): two homologous chromosomes lined up during Meiosis I, recombination may occur

Question 10

Fertilization vs Meiosis?

Answer 10

Fertilization: fusion of sex cells, haploid to diploid
Meiosis: reduction of genetic content by half, diploid to haploid

Question 11

Describe the process of mitosis

Answer 11

Diploid cell –> duplication of chromosomes (form dyads) –> duplicated chromosomes line up in the middle at metaphase –> chromatids pull apart –> cytokinesis

Cell is diploid from start to finish, no increase in ploidy. Mitosis gives genetically identical daughter cells.

Question 12

Describe the process of meiosis I

Answer 12

Diploid cell (2n) –> duplication of chromosomes (form dyads) —> pairs of homologous chromosomes line up in the middle (bivalent) –> crossover may occur –> homologous chromosomes pull apart –> cell constricts to form daughter cells

Reduction from diploid cell to two haploid cells, chromosome number if halved

Question 13

Describe the process of meiosis II

Answer 13

(n) Duplicated chromosomes line up in the middle of cell –> chromatids pull apart –> cell constricts to form daughter cells

Start with two haploid cells from Meiosis I, end with four haploid cells, produce two pairs of gametes

Question 14

What are the different possibilities of gametes?

Answer 14

2^n
n = number of haploid chromosomes
Number of gametes is virtually limitless because of crossing over